This invention relates to a non-aqueous cell of the type using a light metal such as lithium or sodium as the substance for a negative active material.
The cells of this type, owing to the advantage of their high voltage and high energy density, have come to be used as power sources for electronic calculators and electronic watches in the place of silver cells and mercury cells. More recently, they are being adopted as power sources for memories in electronic circuits, particularly as memory backup power sources which are expected to serve during power failure. In this case, the cells are used in the structural system that they will be incorporated into printed-circuit boards similarly to other electronic components. It is, therefore, necessary that connecting tabs should be bonded one each to the positive and negative terminal cases which serve concurrently as positive and negative terminals. Cells of the type of construction described above have been disclosed as by U.S. Pat. No. 4,247,603; Japanese Unexamined Utility Model Publication No. 159,521/1978, for example.
Particularly in the case of non-aqueous cells such as button type non-aqueous cells which are constructed so that negative electrode is pressure-bonded either directly or through the medium of negative-electrode current collector of good thermal conductivity to the inner surface of negative terminal case, when the connecting tab is welded at one end thereof the outer surface of the negative terminal case by the series spot method or the indirect spot method, for example, the portion being welded is heated to temperatures as high as 1000.degree. C. The intense heat, therefore, melts the negative electrode of low melting points (180.degree. C. for lithium and 98.degree. C. for sodium) and consequently melts the separators keeping the positive and negative electrodes apart, with the unfavorable result that the cells suffer occurrence of internal short circuits.
With reference to occurence of deteriorating state of affairs mentioned above, this invention is aimed at preventing the welding of a connecting tab from exerting a thermal effect upon the negative electrode of the cell.